Last week, Bloglines took another step towards transforming the RSS newsreader into a universal inbox with the introduction of its Package Tracking feature - presenting users with the ability to track their UPS package deliveries through notification events from within Bloglines.

By sheer coincidence, I 'd just ordered a Timbuk2 Detour messenger bag from eBags and was able to try the new feature, tracking my purchase through Umkirch, Frankfurt, Barking and Dewsbury. If you'd like to see this for yourself, simply visit my public profile and click the link for UPS Tracking Feed for M1561935154 in the left-hand pane. I'm sure Amazon will follow suit with an order tracking feature.

Services such as Audioscrobbler, Flickr, Buttress and del.icio.us have demonstrated the versatility of RSS as a general purpose notification medium, not simply for text but photos, TV, torrents, URLs and now eCommerce...delivering on the promise of 3rd party notification services explored tentatively by IM operators such as MSN.

However, Bloglines' Package Tracking does underline some of the limitations of RSS. Essentially, designed as a syndication mechanism, RSS is being stretched into application areas that necessitate some form of digital identity and privacy capabilities...subscribing to the UPS feed did not require authentication, hence exposing a potentially private event into the public sphere...if my Hotmail account was leaving an RSS trail, it would be personally very useful in terms of integration with my newsreader, but disastrous for my privacy.

Despite these limitations, which will be resolved in time, RSS has delivered on the vision for web services, offering lightweight interoperability between previously disconnected islands of data.